Cam Position Sensor

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Older Distributor Based Sensor

 In order to convert my Megasquirt system to sequential injection and spark I needed to add a cam position sensor to my engine.  The job of the cam position sensor is to identify when the missing tooth on the crank trigger wheel is for cylinder #1.  The simplest timing setup for a Megasquirt cam position sensor is to produce a single cam position pulse at least one crank wheel tooth prior to the crank wheel missing tooth.  This is the approach that I took.  I wanted a way to produce a pulse once per cam revolution that was timed to occur a few crank wheel teeth prior to the crank missing tooth. 

My first attempt at a cam position sensor was to modify a distributor with electronic pickup to produce this pulse.  This first attempt is linked to on the left side of this page.  I managed to create a working sensor this way but was never happy with the way it looked on the engine and decided not to use it.

I finally located a suitable hall effect sensor that I could mount through a hole in my upper timing cover that does not require a separate magnet.  All this hall sensor needs is a ferrous metal tab to pass within 1mm to 2mm of the sensor to produce a pulse.  This sensor I use is a Hamlin 55075-00-02-A sensor.  The DigiKey part number is 55075-00-02-A-ND.  A copy of the datasheet for this sensor is available in the library.

With a suitable sensor located, I had a spare upper timing cover milled to match the height of my cylinder head.  I did not want to chance ruining my upper timing cover without having a spare available.

Cam position flag shown next to one of the OEM bolt retaining tabs used on the cam gear.

Cam position flag mounted on the cam gear.
I fabricated a simple "tooth" for the sensor to see by bending up a strip of 20ga sheet steel to bolt onto the front of the cam gear.

 

Then it was a straight forward process of locating the correct place to drill the hole for the sensor.  The sensor location is a one shot deal so you need to ensure the proper timing relationship between the cam flag and crank trigger prior to drilling the hole!

I drilled a small 1/8 inch test hole in the timing cover first. This way I can still adjust the final hole location a little if my initial position was incorrect.

Using the 1/8 inch drill bit to test for proper sensor hole position. I managed to get it right on the first try.

With the hole location verified, it was time to drill the 12mm hole.

Sensor installed in timing cover using jam nuts provided with the sensor.

Sensor installed in timing cover using jam nuts provided with the sensor.

Sensor test fit on the engine.

Sensor test fit on the engine. You can see the sensor to flag alignment in this picture.

Final installation of the sensor was done using a liberal amount of red loctite to prevent the inside jam nut from loosening and to seal the sensor hole against oil leaks.  The timing cover is only a few millimeters thick so you need to be careful not to crack the case my over-tightening the sensor nuts.

The last thing I did was a function check of the sensor using my Oscilloscope.  The sensor produces a nice clean 12 volt pulse that Megasquirt can easily detect.

At 1000 RPM the sensor produces a 10ms wide pulse.

The cam position sensor is functional and ready to go.  As soon as I get my MS3x board that contains the separate injector drivers and cam position sensor conditioning circuit I will be all set for sequential.

 

 

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This site was last updated 03/31/10